1. Field of the Invention
This invention relates to a method and device for controlling duplication prevention of an information signal using, for example, an anti-duplication control signal recorded in a recording medium together with the information signal.
2. Description of Related Art
VTR (Video Tape Recorder) has been popularized and a lot of software for being played back on a VTR is available. Recently playback devices and recording/playback devices such as a digital VTR and DVD (Digital Video Disk) have been used practically, and pictures and sound of good quality can be played back and viewed easily.
However, on the other hand, the popularization gives rise to a problem that such abundant software is duplicated without any restriction, and heretofore various duplication prevention measures are available.
For example, though it is not a method for directly inhibiting duplication of analog video signals, a method has been available in which the difference in AGC (Auto Gain Control) system or APC (Auto Phase Control) characteristics between a recording device such as a VTR and a monitor receiver for displaying a picture is utilized to prevent duplication substantially.
In detail, a method in which a VTR performs AGC using a pseudo sync signal inserted in a video signal and a monitor receiver employs AGC system not using the pseudo sync signal is an example of the former method, and in the method, an extraordinarily high level pseudo sync signal is previously inserted as a sync signal for AGC when an analog video signal is recorded in an original recording medium, and then the extraordinarily high level pseudo sync signal is inserted in a video signal supplied from a playback VTR to a recording VTR as a sync signal for AGC.
A method utilizing the difference in APC characteristics in which the APC in a VTR follows a color burst signal in a video signal with a short time constant but the APC in a monitor receiver follows with a relatively long time constant is an example of the latter method, and in the method, the phase of a color burst signal of an video signal is previously inverted partially when analog video signals are recorded in an original recording medium, and then the video signal having the partially inverted color burst signal is output as a video signal supplied from a playback VTR to a recording VTR.
In the case described hereinabove, the monitor receiver which receives supply of the analog video signal from the playback VTR normally plays back a picture without receiving an adverse effect of the partial phase inversion of the color burst signal used for the pseudo sync signal and APC.
However, in the VTR which receives the analog video signal having the inserted pseudo sync signal described hereinabove supplied from the playback VTR or subjected to the phase inversion control of the color burst signal and records the analog video signal in a recording medium, the VTR cannot perform gain control or phase control based on the input signal, and record the video signal not normally. Therefore, a normal picture cannot be viewed when the recorded video signal is played back.
In the case which involves an analog video signal, the above-mentioned methods do not involve duplication inhibition directly, but involve duplication of an abnormal video signal, namely passive duplication prevention control.
On the other hand, in the case which involves a digital information such as a video signal, an anti-duplication control signal such as an anti-duplication code or a duplication generation restriction code is added on a video signal as a digital data and it is recorded in a recording medium in order to inhibit the duplication. This method is regarded as direct duplication prevention control.
For example, FIG. 1 shows a basic structure of a recording device which receives a playback video signal obtained by playing back a recording medium on which a video signal having an added anti-duplication control signal is recorded as described hereinabove, and records (duplicates) the video signal in the recording medium 104.
In the case of this recording device, the recording device receives a playback video signal on which an anti-duplication control signal is added, and the playback video signal is supplied to a write section 101 and anti-duplication control signal detection section 102. The anti-duplication control signal detection section 102 detects the anti-duplication control signal added on the playback video signal, and supplies the detection result to a write control section 103 as duplication prevention control information.
The write control section 103 generates a control signal for controlling the write section 101 based on the supplied duplication prevention control information, and supplies it to the write section 101.
The write section 101 converts the playback video signal to information suitable for recording and writes it in a recording medium 104 for performing recording if the control signal from the write control section 103 permits duplication. On the other hand, the write section 101 does not write the playback video signal in the recording medium 104 if the control signal from the write control section 103 inhibits duplication.
Further, if the anti-duplication control signal detected by means of the anti-duplication control signal detection section 102 permits duplication of only first generation, then the write section 101 converts the video signal to information suitable for recording and writes it in the recording medium 104 for performing recording, and also changes the anti-duplication control signal added as additional information to a duplication inhibition signal (duplication inhibition of next generation), and records it in the recording medium 104. As the result, the video signal cannot be duplicated using the duplicated recording medium 104.
As described hereinabove, in the case that an anti-duplication control signal is added on an information signal transmitted to a recording device, the duplication prevention control such as duplication inhibition is performed consistently in a recording medium using such an anti-duplication control signal.
However, in the case of the recording device described using FIG. 1, a significant lag time is required for detection processing of an anti-duplication control signal in the anti-duplication control signal detection section 102 and for generation processing of a write control signal corresponding to anti-duplication control information in the write control section 103. Further, in the case that an anti-duplication signal is partially changed, more time is required.
From the above, some information signals are already recorded during a time period from starting of duplication, followed by detection of an anti-duplication control signal, to ending of execution of duplication prevention control corresponding to the duplication prevention control content which the detected anti-duplication control signal indicates, and as the result, some information signals are recorded and remain in a recording medium though duplication of the information signal is inhibited.
In the case that it takes, for example, several seconds from the time point of the starting of recording processing to the time point when the duplication prevention control corresponding to an anti-duplication control signal added on an information signal becomes active, it is possible to duplicate the entire information signal by way of successive partial duplication of the information signal repeatedly several seconds by several seconds though duplication of the information signal is inhibited.
A method in which a recording device is controlled so that the information signal is not recorded until the duplication prevention control corresponding to an anti-duplication control signal added on the information signal to be duplicated becomes active is considered as a remedy.
However, in this case, the information signal is not recorded in a recording medium until the duplication prevention control content of the anti-duplication control signal added on the information signal is detected to be duplication-permitted though duplication of the information signal is permitted. This method is disadvantageous in that the initial portion of the information signal is not recorded in a recording medium though duplication of the information signal is permitted.
In view of the above-mentioned problems, the object of the present invention is to provide an information signal duplication prevention method and an information signal duplication prevention device which are capable of perfectly preventing illegal duplication of the information signal.
An information signal recording control device for controlling the recording of an information signal in a recording medium correspondingly to the content of an anti-duplication control signal added on an information signal, wherein the anti-duplication control signal added on the information signal is detected, the recording of the information signal in the recording medium is brought to a stop when the control of the duplication prevention control of the detected anti-duplication control signal is judged to be duplication-inhibited, and at least the information signal recorded by the time the recording of the information signal in the recording medium is brought to a stop is erased from the recording medium.
Further in the present invention, the recording of the information signal is brought to a stop and the recording operation is made impossible thereafter when the content of the duplication prevention control of the anti-duplication control signal is duplication-inhibited.
To solve the above-mentioned problem, the information signal duplication prevention method described regard to an embodiment of the present invention comprises;
a step for detecting an anti-duplication control signal added on an information signal, and
a step for stopping duplication of the information signal and for erasing at least the information signal duplicated in a recording medium by the time the duplication of the information signal is brought to a stop when the duplication prevention control content of the anti-duplication control signal is detected to be duplication-inhibited.
The information signal duplication prevention method described regard to an embodiment of the present invention comprises
a step for detecting an anti-duplication control signal added on an information signal, and
a step for stopping the duplication of the information signal and also for making further duplication operation impossible when the duplication prevention control content of the anti-duplication control signal is detected to be duplication-inhibited.
According to the present invention, duplication of the information signal is brought to a stop and at least the information signal duplicated in a recording medium by the time the duplication of the information signal is brought to a stop is erased when the duplication prevention control content of the anti-duplication control signal added on the information signal to be duplicated is detected to be duplication-inhibited.
In the case that the information signal is partially recorded in a recording medium though the information signal is duplication-inhibited because it takes a certain lag time before the duplication prevention control based on the anti-duplication control signal added on the information signal becomes active, and even though it is an information signal, when it is partially recorded in a recording medium, the information signal recorded on the recording medium is erased. Hence, recording of all the duplication-inhibited information signal by duplicating repeatedly the partial information signals with successive shifting of the portion to be duplicated is prevented. As the result, the duplication of the information signal is prevented consistently and safely correspondingly to the anti-duplication control signal added on the information signal.